Vapor-compression type refrigerating machine and heat exchanger therefor

ABSTRACT

An oil repellent film  31   a  is formed on an inner wall of the tube  31.  By the formation of the oil repellent film  31   a , it becomes possible to prevent refrigerating machine oil remaining in the evaporator  30.  Therefore, a sufficiently large quantity of refrigerating machine oil can be returned to the compressor, and the occurrence of seizing of the compressor can be prevented. As it is possible to prevent refrigerating machine oil remaining in the evaporator  30,  while a reduction in the coefficient of heat transfer between refrigerant and the tube is being prevented, it is possible to prevent a substantial sectional area of the refrigerant path of the tube  31  from decreasing. Therefore, an increase in the pressure loss in the evaporator  30  can be prevented. Accordingly, the heat absorbing property of the evaporator  30  can be enhanced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an evaporator used for a vapor-compression type refrigerating machine in which heat is moved from the low temperature side to the high temperature side. The present invention is effectively applied to a vapor-compression type refrigerating machine having an ejector by which suction pressure of a compressor is increased when expansion energy of refrigerant is converted into pressure energy while the refrigerant is expanded while being decompressed.

[0003] 2. Description of the Related Art

[0004] Usually, in the vapor-compression type refrigerating machine, sliding sections provided in the compressor are lubricated when refrigerant mixed with refrigerating machine oil is circulated in the refrigerating machine.

[0005] Therefore, refrigerating machine oil flows into a heat exchanger, such as an evaporator, together with the refrigerant. When refrigerating machine oil flowing into the heat exchanger stays in the heat exchanger, the following problems may be encountered.

[0006] (1) As a quantity of refrigerating machine oil returning to the compressor is reduced, lubrication of the compressor becomes incomplete, which causes seizing of the compressor.

[0007] (2) Refrigerating machine oil staying in the heat exchanger adheres to the inner walls of the tubes of the heat exchanger, and a substantial sectional area of the refrigerant path is reduced, so that a pressure loss (refrigerant circulating resistance) is increased in the heat exchanger, and the coefficient of heat transfer between the refrigerant and the tubes is decreased. As a result, the heat exchanging capacity of the heat exchanger is lowered.

SUMMARY OF THE INVENTION

[0008] In view of the above problems, the present invention has been accomplished. It is an object of the present invention to solve the above problems described in the above items (1) and (2).

[0009] In order to accomplish the above object, according to an aspect of the present invention, there is provided a heat exchanger applied to a vapor-compression type refrigerating machine, an oil repellent film (31 a) having an oil repelling property being formed on an inner wall face of a tube (31) composing a refrigerant path.

[0010] Due to the foregoing, it is possible to prevent refrigerating machine oil from staying in the heat exchanger (30). Therefore, a sufficiently large quantity of refrigerant machine oil can be returned to the compressor. Accordingly, the occurrence of trouble such as seizing of the compressor can be prevented.

[0011] As it is possible to prevent refrigerating machine oil from staying in the heat exchanger (30), while the coefficient of heat transfer between refrigerant and the tube (31) is prevented from deteriorating, a substantial reduction of the sectional area of the refrigerant path of the tube (31) can be prevented. Therefore, an increase in the pressure loss in the heat exchanger (30) can be prevented, and the heat exchanging capacity of the heat exchanger (30) can be enhanced.

[0012] According to another aspect of the present invention, there is provided a heat exchanger applied to an evaporator, which is one of the heat exchangers provided in a vapor-compression type refrigerating machine and which exhibits a refrigerating capacity by evaporating refrigerant, an oil repellent film (31 a) having an oil repelling property being formed on an inner wall face of a tube (31) composing a refrigerant path.

[0013] Due to the foregoing, it is possible to prevent refrigerating machine oil from staying in the heat exchanger (30). Therefore, a sufficiently large quantity of refrigerant machine oil can be returned to the compressor. Accordingly, the occurrence of trouble such as seizing of the compressor can be previously prevented.

[0014] As it is possible to prevent refrigerating machine oil from staying in the heat exchanger (30), while the coefficient of heat transfer between refrigerant and the tube (31) is prevented from deteriorating, a substantial reduction of the sectional area of the refrigerant path of the tube (31) can be prevented. Therefore, an increase in the pressure loss in the heat exchanger (30) can be prevented, and the heat exchanging capacity of the heat exchanger (30) can be enhanced.

[0015] In this connection, it is preferable that surface tension of material composing the oil repellent film (31 a) is lower than that of refrigerating machine oil mixed with refrigerant.

[0016] It is preferable that material composing the repellent oil film (31 a) is silicon resin or fluororesin.

[0017] According to still another aspect of the present invention, there is provided a vapor-compression type refrigerating machine comprising; a compressor (10) for sucking and compressing refrigerant; a radiator (20) for cooling refrigerant discharged from the compressor (10); an evaporator (30) for evaporating refrigerant so as to absorb heat, composed of a heat exchanger as described before; a nozzle (41) for converting the pressure energy of a refrigerant at high pressure, which has flowed out from the radiator (20), into velocity energy by expanding refrigerant in a reduced pressure; an ejector (40) including a boosting section (42, 43) for boosting the pressure of refrigerant by converting velocity energy into pressure energy when refrigerant of a gas phase, evaporated in the evaporator (30), is sucked by a flow of refrigerant of high velocity injected from the nozzle (41) and then the refrigerant injected by the nozzle (41) and the refrigerant sucked from the evaporator (30) are mixed with each other so as to convert velocity energy into pressure energy; and a gas-liquid separator (50) for separating refrigerant into gas-phase refrigerant and liquid-phase refrigerant and supplying the liquid-phase refrigerant to the evaporator (30) and also supplying gas-phase refrigerant to the compressor (10).

[0018] Due to the foregoing, it is possible to enhance the operating efficiency of the vapor-compression type refrigerating machine.

[0019] In this connection, numbers written in the parentheses after each means represent an example of a corresponding relation of the specific means in the embodiment described later.

[0020] The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawings:

[0022]FIG. 1 is a view showing a model of an ejector cycle relating to an embodiment of the present invention;

[0023]FIG. 2A is a perspective view of an evaporator applied to the ejector cycle relating to the embodiment of the present invention;

[0024]FIG. 2B is a sectional view of a tube;

[0025]FIG. 3 is a view showing a model of the ejector relating to the embodiment of the present invention; and

[0026]FIG. 4 is a p-h diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In this embodiment, an ejector cycle of the present invention is applied to an air-conditioner for vehicle use. FIG. 1 is a view showing a model of the ejector cycle.

[0028] In FIG. 1, the compressor 10 is a well known variable displacement type compressor in which refrigerant is sucked and compressed when power is supplied to the compressor from an engine. The radiator 20 is a heat exchanger on the high pressure side for exchanging heat between refrigerant, which has been discharged from the compressor 10, and outside air so as to cool refrigerant.

[0029] In this connection, as chlorofluorocarbon is used as refrigerant in this embodiment, the pressure of the refrigerant in the radiator 20 is not higher than the critical pressure of the refrigerant. Therefore, the refrigerant is condensed in the radiator 20.

[0030] The evaporator 30 is a heat exchanger on the low pressure side in which heat is exchanged between the air blowing out into a room and the liquid phase refrigerant so that the liquid phase refrigerant can be evaporated and the air blowing out into the room can be cooled.

[0031] In this connection, as shown in FIG. 2A, the evaporator 30 is composed in such a manner that a plurality of tubes 31 composing the refrigerant paths are serpentined and the thin sheet-shaped fins 32, to increase the heat transfer area with respect to air, are joined to the outer faces of the tubes 31.

[0032] As shown in FIG. 2B, on the inner wall face of each tube 31, the oil repellent film 31a having an oil repelling property is formed. This oil repellent films 31 a is made of a material, the surface tension of which is lower than that of refrigerating machine oil. In this embodiment, the oil repellent film 31 a is made of silicon resin or fluororesin.

[0033] In this connection, refrigerating machine oil lubricates sliding sections and other sections provided in the compressor 10. Silicon resin has groups of CH₃, and fluororesin has groups of CF₃ or CF₂.

[0034] In this embodiment, the tube 31 is made of phosphorus deoxidized copper alloy, and the oil repellent film 31 a is made of silicon resin, and the thickness of the film is kept at 0.1 to 3 μm. The oil repellent film 31 a is formed on the tube 31 when the tube 31 is soaked in a solution in which material of the oil repellent film 31 a is dissolved.

[0035] In FIG. 1, the ejector 40 expands refrigerant under the condition that the pressure is reduced, so that the ejector 40 sucks gas-phase refrigerant which has evaporated in the evaporator 30. Further, the ejector 40 converts expansion energy into pressure energy so that the suction pressure of the compressor 10 can be increased.

[0036] In this connection, as shown in FIG. 3, the ejector 40 includes: a nozzle 41 which converts pressure energy of high pressure refrigerant, which flows into the ejector 40, into velocity energy so that refrigerant can be isoentropically expanded under the condition that pressure is reduced; a mixing section 42 for sucking gas-phase refrigerant, which has evaporated in the evaporator 30, by a flow of refrigerant of high velocity injected by the nozzle 41 and mixing it with a flow of refrigerant injected from the nozzle 41; and a diffuser 43 for boosting the pressure of refrigerant by converting velocity energy into pressure energy while refrigerant injected from the nozzle 41 is mixed with refrigerant sucked from the evaporator 30.

[0037] In this embodiment, in order to increase the velocity of refrigerant jetting out from the nozzle 41 to a value not lower than the sound velocity, a Laval nozzle is adopted which has a throat section, the path area of which is the smallest, in the middle of the path.

[0038] In the mixing section 42, mixing is conducted so that a sum of the momentum of a flow of refrigerant injected from the nozzle 41 and the momentum of a flow of refrigerant sucked from the evaporator 30 to the ejector 40 can be preserved. Therefore, static pressure is increased even in the mixing section 42. On the other hand, in the diffuser 43, when the sectional area of the path is gradually increased, a dynamic pressure of refrigerant is converted into a static pressure. Therefore, in the ejector 40, the pressure of refrigerant is increased in both the mixing section 42 and the diffuser 43. Therefore, the mixing section 42 and the diffuser 43 are generically called a boosting section.

[0039] In FIG. 1, the gas-liquid separator 50 is a gas-liquid separating means into which refrigerant flows after it has flowed out from the ejector 40, and the refrigerant, which has flowed into the gas-liquid separator 50, is separated to gas-phase refrigerant and liquid-phase refrigerant, and the thus separated liquid-phase refrigerant is stored. An outlet for gas-phase refrigerant of the gas-liquid separator 50 is connected with the suction side of the compressor 10, and an outlet for liquid-phase refrigerant of the gas-liquid separator 50 is connected with the entry side of the evaporator 30.

[0040] In this connection, FIG. 4 is a diagram showing a relation between p (absolute pressure of refrigerant) and h (specific enthalpy). In this diagram, the overall macro operation of the ejector cycle is shown. This macro operation of the ejector cycle is the same as that of the well-known ejector cycle. Therefore, in this embodiment, an explanation of the overall macro operation of the ejector cycle are omitted. In this connection, mark  shown in FIG. 4 represents a state of refrigerant at a position indicated by mark  in FIG. 1.

[0041] Next, characteristics of this embodiment will be described as follows.

[0042] In this embodiment, as the oil repellent film 31 a is formed on the inner wall of each tube 31, it is possible to prevent refrigerating machine oil from staying in the evaporator 30. Therefore, a sufficiently large quantity of refrigerant machine oil can be returned to the compressor 10. Accordingly, the occurrence of trouble such as seizing of the compressor 10 can be prevented.

[0043] As it is possible to prevent refrigerating machine oil from staying in the evaporator 30, while the coefficient of heat transfer between refrigerant and the tube (31) is prevented from deteriorating, a reduction of the substantial sectional area of the refrigerant path can be prevented. Therefore, an increase in the pressure loss in the evaporator 30 can be prevented, and the heat absorbing capacity of the evaporator 30 can be enhanced.

[0044] In the vapor-compression type refrigerating machine in which the pressure of refrigerant is isoentropically reduced by a pressure reducing means such as an expansion valve (This cycle will be referred to as an expansion valve cycle, hereinafter.), refrigerant which has flowed out from the expansion valve flows into the evaporator. On the other hand, in the ejector cycle, as shown in FIG. 1, refrigerant which has flowed out from the ejector 40 flows into the gas-liquid separator 50, and liquid phase refrigerant separated by the gas-liquid separator 50 is supplied to the evaporator 30, and gas phase refrigerant separated by the gas-liquid separator 50 is sucked into the compressor 10.

[0045] In other words, in the expansion valve cycle, there is one refrigerant flow in which refrigerant circulates in the order of compressor→radiator→expansion valve→evaporator→compressor. On the other hand, in the ejector cycle, there are two refrigerant flows. In one flow, refrigerant flows in the order of compressor 10→radiator 20→ejector 40→gas-liquid separator 50→compressor 10 (This flow will be referred to as a driving flow, hereinafter.). In the other flow, refrigerant flows in the order of gas-liquid separator 50→evaporator 30→ejector 40→gas-liquid separator 50 (This flow will be referred to as a sucking flow, hereinafter.).

[0046] In this case, the driving flow is made to circulate by the compressor 10. On the other hand, the sucking flow 10 is made to circulate by a boosting action generated by the ejector 40, that is, the sucking flow 10 is made to circulate by a pump action generated by a difference in pressure between the outlet of refrigerant of the ejector 40 and the inlet of liquid phase refrigerant of the ejector 40. Accordingly, when a flow rate of the driving flow is decreased and a boosting action generated by the ejector 40 is reduced, a flow rate of refrigerant of the sucking flow is decreased. Therefore, refrigerating machine oil, which has flowed into the evaporator 30 together with liquid phase refrigerant, tends to stay in the evaporator 30.

[0047] On the other hand, in the expansion cycle, refrigerant is directly sucked from the evaporator by the compressor. Therefore, even when a heat load is decreased, it is difficult for refrigerating machine oil to stay in the evaporator compared with the ejector cycle. Accordingly, it is especially effective for the present invention to be applied to the evaporator 30 provided in the ejector cycle.

[0048] In the above embodiment, the present invention is applied to an evaporator provided in the ejector cycle. However, it should be noted that the present invention is not limited to the above specific embodiment. It is possible to apply the present invention to an evaporator provided in the expansion valve cycle.

[0049] It is possible to apply the present invention to any type evaporator 30, that is, the present invention can be applied to a serpentine type heat exchanger in which the tube 31 is snaked. Also, the present invention can be applied to a multi-flow type heat exchanger composed of a plurality of tubes, header tanks and others.

[0050] In the above embodiment, the vapor-compression type refrigerating machine, in which the ejector of the present invention is used, is applied to an air-conditioner for vehicle use. However, the present invention is not limited to the above specific application.

[0051] In the above embodiment, the present invention is applied to an evaporator. However, it should be noted that the present invention is not limited to the above specific embodiment. It is possible to apply the present invention to a heat exchanger on the high pressure side such as a radiator 20. 

1. A heat exchanger applied to a vapor-compression type refrigerating machine, an oil repellent film having an oil repelling property being formed on an inner wall face of a tube composing a refrigerant path.
 2. A heat exchanger applied to an evaporator, which is one of the heat exchangers provided in a vapor-compression type refrigerating machine and exhibits a refrigerating capacity by evaporating refrigerant, an oil repellent film having an oil repelling property being formed on an inner wall face of a tube composing a refrigerant path.
 3. A heat exchanger according to claim 1, wherein surface tension of material composing the oil repellent film is lower than that of refrigerating machine oil mixed with refrigerant.
 4. A heat exchanger according to claim 1, wherein material composing the oil repellent film is silicon resin or fluororesin.
 5. A vapor-compression type refrigerating machine using an ejector, comprising; a compressor for sucking and compressing refrigerant; a radiator for cooling refrigerant discharged from the compressor; an evaporator for evaporating refrigerant so as to absorb heat, composed of a heat exchanger described in claim 1; a nozzle for converting pressure energy of refrigerant of high pressure, which has flowed out from the radiator, into velocity energy by expanding refrigerant in a reduced pressure; an ejector including a boosting section for boosting the pressure of refrigerant by converting velocity energy into pressure energy when refrigerant of gas phase evaporated in the evaporator is sucked by a flow of refrigerant of high velocity injected from the nozzle and then refrigerant injected by the nozzle and refrigerant sucked from the evaporator are mixed with each other so as to convert velocity energy into pressure energy; and a gas-liquid separator for separating refrigerant into gas-phase refrigerant and liquid-phase refrigerant and supplying the liquid-phase refrigerant to the evaporator and also supplying gas-phase refrigerant to the compressor. 